1) Basic IAB Counterpulsation Principles and Limitations:
Intra-Aortic balloon (IAB) assist devices are devices used to assist the pumping function of a failing heart. In their simpler application they are comprised of a pneumatic pump system inflating and deflating a balloon periodically. The balloon is positioned in the aorta and gated with the failing heart in counterpulsation mode. Gating is such that balloon deflates when the heart is in systole, and inflates when the heart is in diastole. The principle behind counterpulsation relies on the following facts:                1. During systole, deflation of the balloon creates an empty space within the aorta which ‘vacuums’ blood out of the Left Ventricle (LV). Drawing blood from the LV assists the effort of the failing heart to pump out blood (“after-load decrease”).        2. During diastole, whilst the aortic valve is closed and the LV is receiving blood for the next cardiac cycle, the balloon inflates within the aorta. The previously blood-filled aortic space is abruptly occupied by the inflated balloon, which raises the pressure in the aorta and ejects blood towards all directions, apart from into the heart, thus augmenting circulatory blood flow.        
In order for an IAB to be clinically effective, meaning to accomplish a reasonable cardiac after-load decrease and at least a 30% aortic pressure augmentation in a 1.80 m patient, a balloon volume of at least 34 mLs displacement volume is usually used. Given the fact that the LV pumps out an average of 70 mLs in every heartbeat, this displacement volume of 34 mLs represents about half of that volume (˜ 34/70=49% ejection fraction). It is easily understood that if the current IAB was a perfect “LV suction pump” system, it would be expected to draw all its 34 mLs displacement volume from the LV and thus achieve easily a ˜50% ejection fraction during deflation Equally it would be expected to achieve a similar 50% pressure assist effect on the beating heart. Instead, existing devices typically achieve only about a 10-20% pressure assist effect. This is disproportionate.
The disparity between balloon volume and pressure assist effect is largely due to four specific facts, each one of which contributes independently to the IAB's pressure wave loss:                1. The initially transverse direction of the inflated balloon's expansion pulse wave, which creates energy loss through a shock wave exerted on the aorta, prior to generating an effective axial pulse wave.        2. The elastic properties of the aorta, which absorbs a substantial portion of the pulse wave energy generated by the balloon.        3. The distance of the IAB from the heart, which in combination with the facts (1) and (2) result in “waste” of a large proportion of the balloon's pressure wave through absorption of the pulse waves within the aorta. It is important to stress that current IAB designs prohibit placement within the Aortic arch, as it would cause severe “whipping” trauma upon inflation of the balloon.        4. Most importantly, undesired retrograde flow during the balloon's deflation, from the lower abdominal and iliac circulation, which absorbs almost half of the IAB's desired vacuum effect on the heart.        
Although a large balloon counterpulsation volume could be used in an effort to provide a desired level of pressure augmentation, other important factors co-exist, posing additional burdens.
It is well known, to those familiar with the art, that the IAB is percutaneously inserted as a folded structure through an incision in a major peripheral artery, such as the femoral artery, measuring 4-7 mm. The IAB is connected to a helium pump through a balloon catheter which cyclically supplies helium into and vacuums helium from the IAB during inflation and deflation. The diameter of the catheter doesn't usually exceed the 2.5-3 mm due to the associated arterial trauma and the compromise of femoral circulation from the space occupied by the balloon catheter. It is therefore obvious that although large balloon volumes could be accomplished with a bigger balloon catheter size, this is limited by the arterial diameter at the insertion site.
2) Limitations in the use of IAB in Non-Cardiac Pathologies:
Despite the IAB's burdens described above, IAB is yet able to assist cardiac pumping function, improve cardiac output, and increase coronary blood supply to the heart. There are also a number of non-cardiac clinical conditions in which pressure or flow augmentation in the circulation would be desirable. Some of the most common are: ischemic stroke, renal failure, and ischemic bowel. Many of these conditions are typically encountered in certain clinical context of low perfusion pressures, such as that of the post-operative cardiac surgery patient, due to the perioperative low blood flow during Cardiopulmonary By Pass (CPB). The more compromised the blood flow is in a particular body organ pre-operatively (due to diabetes, atherosclerosis, etc.), the more vulnerable it is to develop ischemia post-operatively due to the low pressure blood flows during the operation. As a result stroke, renal failure, and bowel necrosis may occur post-operatively, in a percentage as high as 30%, depending on the actual age range and the underlying susceptibility to ischemia of the population group under study. Although IAB pressure augmentation would be a reasonable approach to treat all the clinical groups mentioned above, in clinical reality this doesn't occur. This is attributed to some particularities related to the IAB insertion and operation: In order to have a 20% increase in aortic pressure augmentation—e.g., for sufficient bowel and brain perfusion, a ‘big’>34 mLs balloon is usually used. Unfortunately this also translates to a 2-3 mm diameter balloon catheter and an increased clinical risk of amputation due to femoral blood flow compromise. There is also a risk of aortic trauma and ischemic renal failure due to the whipping effect of the IAB upon the wall of the descending aorta, which has also been shown to induce intermittent flow blockade of the renal arteries. Those drawbacks have limited expansion of the clinical applicability of IAB and as a consequence, by weighing risks and benefits, IABs have been reserved mainly for ischemic heart disease patients.
3) Prior Art:
Several attempts have been made, for instance in U.S. Pat. Nos. 4,522,195 and 4,785,795, to combine a pumping balloon with a valve system, most frequently a second balloon, as in U.S. Pat. No. 6,210,318, that acts like a valve operatively coupled to the main balloon. This second balloon achieves to some extent compartmentalization of the pressure augmentation effect of the main balloon, as it keeps the pressure effect on ‘one desired side’ of where the IAB resides. This approach ‘halves’ the demand for balloon volume (by achieving a better vacuum effect), augments the balloon pressure effect, decreases the demand for a big catheter tube that would be needed for a bigger balloon, and limits many of the drawbacks above. However additional problems with this approach do occur. For instance the second ‘valve’ balloon has to be very ‘close’ to the aorta in order to achieve flow occlusion, and has to be fluidically connected to the main balloon. This proximity along with the repetition of the second balloon's inflation/deflation occlusion cycles presumably results in significant wall trauma and thus it is not surprising that those approaches have not been successful yet in any clinical setting.